1. Technical Field
This disclosure relates to an air cleaner.
2. Related Art
An air cleaner is provided midway through an air flow passageway, for example, to filter the air flowing through the inside of the air flow passageway. Such an air cleaner is used in a stretch of air flow passageway, such as an intake system of an internal combustion engine for a car, an air-conditioning system or a cooling air delivery system. In an air flow passageway having such an air cleaner, noise coming from noise source such as an engine, a fan or a motor propagates inside the air flow passageway. In such an air flow path, air column resonance occurs in the duct system connected to the air cleaner. Therefore, there has been a demand for reducing noise propagating inside the air flow passageway.
A technique for reducing noise propagating through an air flow passageway, which has been developed or put into practical use, includes a technique in which the air cleaner in the air flow passageway itself is utilized as an expansion chamber, a technique in which a resonance-type silencer, such as a Helmholtz resonator, is provided in the duct or in the air cleaner, and a technique in which a sound-absorbing material is provided.
For example, JP-A-09-88749 discloses a technique in which a sound-absorbing material is provided at the connecting portion between the air cleaner and the air intake duct. JP-UM-A-06-076651 discloses a technique in which a sound-absorbing material is placed along the case inner surface of the air cleaner. In the technique described in JP-UM-A-06-076651, a sound-absorbing material is covered with a water-impermeable membrane.
A technique called “porous duct” has been known in the art as a technique for suppressing air column resonance occurring in a duct system connected to an air cleaner. According to this technique, an air-permeable portion is provided in a part of the duct wall formed from a non-air-permeable material. A porous duct is an attempt to reduce noise propagating through the duct by preventing the air column resonance in the duct system. For example, as a porous duct, the technique described in JP-A-2001-323853 is known in the art. A characteristic feature of this technique lies in a porous material, such as a non-woven fabric, having a moderate air-permeability attached to the duct wall so as to cover a hole provided in the middle section of the non-air-permeable duct wall. Thus, the space inside the duct and the outside space are brought into communication with each other through the porous material. Moreover, a porous duct described in JP-A-2001-323853 includes a non-woven fabric that is heat-welded to an opening at the tip of a small tubular portion that is provided so as to project from the wall surface of the duct body. With such a duct, it is possible to suppress the occurrence of air column resonance in the duct system by adjusting the air permeability of the porous material. Thus, it is possible to reduce noise propagating through the duct system. This also provides an advantage that a non-woven fabric can be easily attached, and an advantage that the air flow resistance of the duct can be reduced.